Abstract:The reaction of OH radicals with acetic acid 2‐hydroxyethyl ester, (1), in aqueous solutions has been studied. A rate constant of k(OH + 1) = 8.5 · 108 M−1 s−1 was obtained. The transients a few μs after pulse consist of ∼83% formylmethyl radicals, CH2CHO, the remainder being mainly CH3C(O)OCHCH2OH radicals, (3). γ‐radiolysis of 1 in N2O saturated aqueous solutions led to G(acetic acid)=5.0 without contribution of a chain reaction. It is concluded that the OH attack on 1 leads mainly to the redical CH3C(O)OCH2… Show more
“…This observation is in agreement with pulse radiolytic studies of ethylene glycol derivatives by Schulte-Frohlinde. He could show that elimination of acetic acid occurs in neutral aqueous solution about 10 3 times faster than elimination of water (Scheme ).…”
Ribonucleotide reductases are enzymes that catalyze the
conversion of ribonucleotides to 2‘-deoxyribonucleotides. This important reaction is initiated by the generation
of a C-3‘ nucleotide radical and subsequent loss
of the 2‘-hydroxyl group. In order to model certain steps in this
mechanism, selenol ester 23 was prepared and
photolyzed providing the first selective chemical access to the
3‘-adenosyl radical. From product analysis it could
be shown that elimination of the 2‘-OH function readily takes place
under general base catalysis. The rate coefficient
for this reaction was determined by competition kinetics to be
1.5·106 s-1 in the
presence of 1 M triethylammonium
acetate buffer at pH 7. Without catalyst the elimination rate is
about 103 times slower. It can be concluded that
a
similar mechanism is also feasible for the key steps of the enzyme
catalyzed reaction.
“…This observation is in agreement with pulse radiolytic studies of ethylene glycol derivatives by Schulte-Frohlinde. He could show that elimination of acetic acid occurs in neutral aqueous solution about 10 3 times faster than elimination of water (Scheme ).…”
Ribonucleotide reductases are enzymes that catalyze the
conversion of ribonucleotides to 2‘-deoxyribonucleotides. This important reaction is initiated by the generation
of a C-3‘ nucleotide radical and subsequent loss
of the 2‘-hydroxyl group. In order to model certain steps in this
mechanism, selenol ester 23 was prepared and
photolyzed providing the first selective chemical access to the
3‘-adenosyl radical. From product analysis it could
be shown that elimination of the 2‘-OH function readily takes place
under general base catalysis. The rate coefficient
for this reaction was determined by competition kinetics to be
1.5·106 s-1 in the
presence of 1 M triethylammonium
acetate buffer at pH 7. Without catalyst the elimination rate is
about 103 times slower. It can be concluded that
a
similar mechanism is also feasible for the key steps of the enzyme
catalyzed reaction.
“…The β-C,O bond scission of substituted glycol radicals, generated by γ-radiolysis in aqueous solution, was studied as a model for the radical-induced cleavage of DNA. Schulte-Frohlinde and co-workers observed fast β-elimination for 2-acetoxy-1- hydroxy -1-ethyl radical ( 5 ) whereas Gilbert, Larkin, and Norman, found slower elimination of the β-acetate group from 2-acetoxy-1- methoxy -1-ethyl radical ( 6 ). 1 …”
Precursors for the selective generation of C-2 glyceryl radicals
were synthesized, and the chemical behavior
of the corresponding radicals was investigated by ESR spectroscopy,
product analysis, and kinetic measurements. It
was found that cleavage of the β-C,O bond proceeds rapidly, if a
hydroxyl group is present at the radical carbon
center. The rate constant for the elimination of a β-acetoxy
group from radical 30 was dependent on the solvent
(k
E
= 4 × 105 s-1 in methanol,
k
E = 2 × 107
s-1 in toluene). With these results and
ab
initio calculations a concerted
elimination mechanism is suggested. α-Methoxy-substituted C-2
glyceryl radicals 42 and 43 showed
heterolytic
β-C,O bond cleavage under formation of radical cations. With
ester-substituted radicals 24 and 35 no
elimination
could be observed. To demonstrate the biological significance of
these findings, C-2 lysolecithin radical 53 was
generated, which led to fast β-elimination.
“…* From this value a G value for the formation of acetic acid from reaction (4) followed by reaction (1) of 4.5 was obtained which is slightly lower than the one reported earlier 1 . From the lower value a value for the percent of OH attack at the 2' position of 3 of ~75% is derived.…”
Section: Oh + 3 -» Radicals + H20 (4)mentioning
confidence: 64%
“…This reaction sequence is excluded because it is not in accord with conclusions drawn from transient UV spectra 1 and from ESR measurements 39 The absence of a solvent isotope effect now permits the exclusion of two of the following three conceivable modes of the heterolytic decay of 1. We first consider the simultaneous fragmentation of 1 into H®, CH3COO® and 2, as symbolized by reaction (9).…”
Section: A Solvolysis Of 1 Leading Immediately To Ions Reaction (7)mentioning
confidence: 99%
“…In a recent paper 1 we described the fast elimination of acetic acid from acetic acid 2-hydroxyethyl ester 2-yl (1) to yield the formylmethyl radical (2) according to tbe overall reaction (1).…”
Radical Decay Mechanism, Acetic Acid Elimination, Pulse Radiolysis, Conductivity Changes, Acetic Acid 2-Hydroxyethyl EsterFrom conductivity changes following a 1 ^s electron pulse applied to N20 saturated H2O or D2O solutions of acetic acid 2-hydroxyethyl ester the rate constants of the monomolecular decay of the radical HO-CH-CH2-OCOCH3 (1) in H20 and of DO-CH-CH2-OCOCH3 in D2O were derived, reaction (1).
HO-CH-CH2-OCOCH3 -> CH2CHO + CH3COO-+ H+ (1) 1A value of k\ of 5.5 • 10 5 s -1 ± 25%, at 22 to 24 °C, independent of the above solvents and of pH (or pD) was obtained. It is concluded that the rate determining step of reaction (1) is the heterolytic fragmentation of the carbon acetate bond in 1 followed by formation of H+.
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